Add shutdown hook

src/main/java/it/tdlight/client/SimpleTelegramClient.java

@@ -174,6 +174,18 @@ public final class SimpleTelegramClient implements Authenticable {
 		this.authenticationData = authenticationData;
 		createDirectories();
 		client.initialize(this::handleUpdate, this::handleUpdateException, this::handleDefaultException);
+
+		// Handle unexpected shutdown
+		Runtime.getRuntime().addShutdownHook(new Thread(() -> {
+			try {
+				// Send close function
+				this.client.send(new TdApi.Close(), ok -> {}, ex -> {});
+				// Wait until the client has been closed successfully
+				this.waitForExit();
+			} catch (Throwable ignored) {
+				// Ignore errors since we are shutting down everything
+			}
+		}));
 	}
 
 	private void createDirectories() {